1. Field of the Invention
This invention relates generally to semiconductor processing, and more particularly to an apparatus and method for delivering gas to a vacuum processing chamber.
2. Description of the Related Art
Vacuum chambers are used in a myriad of applications in semiconductor processing. Chemical vapor deposition, physical vapor deposition, etching, rapid thermal processing and scanning electron microscopy represent just a few of the types of applications that require reduced pressure environments. Although the specific components in vacuum processing systems vary widely depending upon the particular application, most such systems incorporate a vacuum chamber and one or more gas supply lines that are used to deliver various types of gases to the vacuum chamber. Depending upon the application, the gases may be etchants, chemical vapor deposition reaction products, inert flushing gases, oxidizing ambients or other types of gases. The processing gases may be delivered from discrete cylinders, or via more complex delivery systems depending upon the gaseous species.
The flow of gases into the vacuum processing chamber is controllled by a valve. In many cases, a flow restrictor, such as a mass flow controller, and a pressure relief valve are used in conjunction with the gas supply valve. Gas supply valves are manufactured in a variety of different arrangements, such as needle valves, disk valves and flap valves to name just a few. Regardless of the particular configuration, the, opening of the gas supply valve involves the unseating of a member, e.g., a diaphragm seat, from a fully closed position to an open position to enable the gas flow through an orifice and into the vacuum chamber. Most gas supply valves are biased to a fully closed position by a spring, bellows arrangement, or other type of biasing member. The opening of the valve involves application of a force to overcome the spring bias to unseat the valve member.
In many types of gas supply valves, the spring bias is overcome by manually or otherwise turning a handle on a valve stem or otherwise applying an axial force to the valve stem. One example of these is a solenoid actuated valve. Other types of gas supply valves are fluid actuated. In these types of designs, the unseating of the valve member is accomplished by supplying a pressurized fluid via a pilot line to a portion of the valve to overcome the closing force of the valve""s biasing member. A pilot line supply valve is opened to deliver pilot pressure to and open the fluid actuated gas supply valve. Fluid actuated valves are favored in applications involving potentially explosive processing gases and/or where positive and complete shut-off is required for process isolation.
The pressure differentials between the gas supply line and the vacuum processing chamber can be quite large and produce a phenomenon known as pressure burst. The initial opening of the gas supply valve results in an instantaneous burst of gas into the vacuum processing chamber. This burst of gas into the chamber can dislodge particulates from the walls of the vacuum chamber and from the sides and bottom of the semiconductor wafer. These liberated particulates can settle on the critical circuit structures of the wafer as contaminates and lead to yield problems. Pressure burst may also lead to process variations across the surface of the wafer due to the irregular movement of gases through the vacuum chamber.
The problem of pressure burst stems largely from the fact that the opening of the gas supply valve constitutes a gross mechanical movement in many conventional vacuum processing systems. For example, in conventional vacuum processing chamber systems employing fluid actuated gas supply valves, the opening of the gas supply valve entails the rapid delivery of full pilot line pressure to the gas supply valve. This near instantaneous delivery of full pilot pressure to the fluid actuated supply valve is necessary to ensure that the fluid actuated supply valve unseats and moves to an open position. Most operators deliver a pilot line pressure that is well in excess of the factory specified minimum opening pressure for the fluid actuated gas supply valve. This is due to the fact that pilot actuated supply valves may exhibit a higher minimum opening pressure than factory specified as a result of manufacturing variations or unanticipated wear. To provide the requisite pilot line pressure, the pilot line supply valve is rapidly moved to a fully open position. Little attempt is made to modulate the flow of pilot line fluid to the fluid actuated gas supply valve. As a result, any residual pressure behind the fluid actuated gas supply valve can rapidly dump into the vacuum processing chamber.
The present invention is directed to overcoming or reducing the effects of one or more of the foregoing disadvantages.
In accordance with one aspect of the present invention, a processing apparatus is provided that includes a vacuum processing chamber, a first source of gas coupled to the vacuum processing chamber, and a fluid actuated valve for regulating the flow of the gas from the first source of gas to the vacuum processing chamber. The fluid actuated valve is operable to open in response to a flow of an actuating fluid and has a minimum valve opening pressure. Means are provided for selectively modulating the flow of the actuating fluid to the fluid actuated valve whereby the pressure of the actuating fluid is increased incrementally from an initial pressure to at least the minimum valve opening pressure.
In accordance with another aspect of the present invention, a processing apparatus is provided that includes a vacuum processing chamber, a first source of gas coupled to the vacuum processing chamber, and a fluid actuated valve for regulating the flow of the gas if from the first source of gas to the vacuum processing chamber. The fluid actuated valve is operable to open in response to a flow of an actuating fluid and has a minimum valve opening pressure. A valve is provided for enabling the actuating fluid to flow to the fluid actuated valve. A controller is provided for selectively modulating the flow of the actuating fluid to the fluid actuated valve whereby the pressure of the actuating fluid is increased incrementally from an initial pressure to at least the minimum valve opening pressure.
In accordance with another aspect of the present invention, a method is provided of introducing a gas into a chamber via a fluid actuated supply valve that has a minimum opening pressure and is in fluid communication with a supply of actuating fluid. An initial gas pressure in the chamber is sensed. A flow of actuating fluid to the fluid actuated supply valve is cycled on and off X cycles to gradually increase the pressure of the actuating fluid to at least the minimum opening pressure. The gas pressure in the chamber is sensed again and the fluid actuated supply valve is opened if the gas pressure in the chamber is greater than the initial gas pressure.